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United States Patent |
5,604,307
|
Iida
,   et al.
|
February 18, 1997
|
Tire pressure drop alarm device sensing partial travel on irregular road
surface
Abstract
A tire pressure drop alarm device for judging a pneumatic pressure drop by
calculating rotational angular velocities of tires provided for a
four-wheel vehicle. When the vehicle is traveling on a road which varies
in condition between left and right sides, a front/rear ratio of
rotational angular velocities of the tires at the shoulder side of the
road changes more markedly than that of rotational angular velocities of
the tires at the center side, and a large time differential value appears.
Therefore, it is possible to judge the traveling condition of the vehicle
when the road condition varies between left and right sides. When it is
judged that the traveling condition of the vehicle encounters a road
condition which varies between left and right sides, the tire rotation of
the four wheels is likely to become unbalanced, giving a false alarm even
if the tire pressure does not drop. In this case, the judgment by the
pneumatic pressure drop judging means is inhibited to prevent an issuance
of a false alarm.
Inventors:
|
Iida; Akiko (Osaka, JP);
Nakajima; Mikao (Osaka, JP);
Horie; Hiroto (Akashi, JP)
|
Assignee:
|
Sumitomo Rubber Industries, Ltd. (Osaka, JP)
|
Appl. No.:
|
593370 |
Filed:
|
January 29, 1996 |
Foreign Application Priority Data
Current U.S. Class: |
73/146.2; 340/444 |
Intern'l Class: |
B60C 023/02 |
Field of Search: |
73/146.2,146.5
340/444
364/558
|
References Cited
U.S. Patent Documents
3691524 | Sep., 1972 | Frost et al. | 340/444.
|
4876528 | Oct., 1989 | Walker et al. | 340/444.
|
5343741 | Sep., 1994 | Nishihara et al.
| |
Foreign Patent Documents |
0489562 | Jun., 1992 | EP | 340/444.
|
4337443 | Nov., 1993 | DE.
| |
4410941 | Mar., 1994 | DE.
| |
63-305011 | Dec., 1988 | JP.
| |
4-11844 | Jan., 1992 | JP.
| |
4-212609 | Aug., 1992 | JP.
| |
2191553 | Jun., 1987 | GB.
| |
Primary Examiner: O'Shea; Sandra L.
Assistant Examiner: Felber; Joseph L.
Attorney, Agent or Firm: Rabin, P.C.; Steven M.
Claims
We claim:
1. A tire pressure drop alarm device, comprising:
rotational angular velocity calculating means for calculating rotational
angular velocities of tires provided for corresponding wheels of a
four-wheel vehicle having a front left wheel, a front right wheel, a rear
left wheel and a rear right wheel;
pneumatic pressure drop judging means for judging whether a tire pressure
drops, based on the rotational angular velocities calculated by the
rotational angular velocity calculating means;
alarm means for generating a signal corresponding to a judgment result
output of the pneumatic pressure drop judging means;
operating means for determining a first time differential value of a
front/rear wheel ratio of the rotational angular velocities of the left
tires and a second time differential value of a front/rear wheel ratio of
the rotational angular velocities of the right tires, and determining a
difference between the first time differential value and the second time
differential value;
one-sided irregular road traveling judging means for judging a traveling
condition of the vehicle, to determine a variation in road conditions
between left and right sides of the vehicle, based on the difference
between the first time differential value and the second time differential
value determined by the operating means when the vehicle is operating
under one-sided irregular road traveling conditions, and for generating a
judgment result output; and
means for inhibiting the pneumatic pressure drop judging means when the
one-sided irregular road traveling judging means indicates a variation in
road conditions between left and right sides of the vehicle.
2. A tire pressure drop alarm device according to claim 1, wherein the
one-sided irregular road traveling judging means comprises means for
performing integral processing on the difference between the first time
differential value and the second time differential value determined by
the operating means to generate a value upon which the traveling condition
of the vehicle is judged.
3. A tire pressure drop alarm device according to claim 2, wherein the
one-sided irregular road traveling judging means determines a variation in
road conditions exists between the left and right sides of the vehicle,
when the value generated by the integral processing means is greater than
a predetermined threshold value t.sub.1 ; and determines a variation in
road conditions does not exist between the left and right sides of the
vehicle when the value generated by the integral processing means becomes
smaller than a predetermined threshold value t.sub.2, wherein t.sub.1 is
greater than t.sub.2.
4. A tire pressure drop alarm device according to claim 1, wherein the
one-sided irregular road traveling judging means determines a variation in
road conditions exists between the left and right sides of the vehicle,
when the difference between the first time differential value and the
second time differential value determined by the operating means is
greater than a predetermined threshold t.sub.1 ; and determines a
variation in road conditions does not exist between the left and right
sides of the vehicle when the difference between the first time
differential value and the second time differential value becomes smaller
than a predetermined threshold value t.sub.2, wherein t.sub.1 is greater
than t.sub.2.
5. A tire pressure drop alarm device, comprising:
rotational angular velocity calculating means for calculating rotational
angular velocities of tires provided for corresponding wheels of a
four-wheel vehicle having a front left wheel, front right wheel, a rear
left wheel, and a rear right wheel;
pneumatic pressure drop judging means for judging whether a tire pressure
drops, based on the rotational angular velocities calculated by the
rotational angular velocity calculating means;
alarm means for generating a signal corresponding to a judgment result
output of the pneumatic pressure drop judging means;
operating means for determining a first front/rear ratio of the rotational
angular velocities of the left tires and a second front/rear ratio of the
rotational angular velocities of the right tires, and determining a time
differential value of a difference between the first front/rear wheel
ratio and the second front/rear ratio;
one-sided irregular road traveling judging means for judging a traveling
condition of the vehicle to determine a variation in road conditions
between left and right sides of the vehicle, based on the differential
value of the difference between the first front/rear wheel ratio and the
second front/rear wheel ratio determined by the operating means when the
vehicle is operating under one-sided irregular road traveling conditions,
and for generating a judgment result output; and
means for inhibiting the pneumatic pressure drop judging means when the
one-sided irregular road traveling judging means indicates a variation in
road conditions between left and right sides of the vehicle.
6. A tire pressure drop alarm device according to claim 5, wherein the
one-sided irregular road traveling judging means comprises means for
performing integral processing on the time differential value of the
difference in the first front/rear wheel ratio and the second front/rear
wheel ratio determined by the operating means to generate a value upon
which the traveling condition of the vehicle is judged.
7. A tire pressure drop alarm device according to claim 6, wherein the
one-sided irregular road traveling judging means determines a variation in
road conditions exists between the left and right sides of the vehicle,
when the value generated by the integral processing means is greater than
a predetermined threshold value t.sub.1 ; and determines a variation in
road conditions does not exist between the left and right sides of the
vehicle when the value generated by the integral processing means becomes
smaller than a predetermined threshold value t.sub.2, wherein t.sub.1 is
greater than t.sub.2.
8. A tire pressure drop alarm device according to claim 5, wherein the
one-sided irregular road traveling judging means determines a variation in
road conditions exists between the left and right sides of the vehicle,
when the time differential value of the difference between the first
front/rear wheel ratio and the second front/rear wheel ratio determined by
the operating means is greater than a predetermined threshold value
t.sub.1 ; and determines a variation in road conditions does not exist
between the left and right sides of the vehicle when the time differential
value of the difference between the first front/rear wheel ratio and the
second front/rear wheel ratio becomes smaller than a predetermined
threshold value t.sub.2, wherein t.sub.1 is greater than t.sub.2.
9. A tire pressure drop alarm device, comprising:
rotational angular velocity calculating means for calculating rotational
angular velocities of tires provided for corresponding wheels of a
four-wheel vehicle having a front left wheel, a front right wheel, a rear
left wheel, and a rear right wheel;
pneumatic pressure drop judging means for judging whether a tire pressure
drops, based on the rotational angular velocities calculated by the
rotational angular velocity calculating means;
alarm means for generating a signal corresponding to a judgment result
output of the pneumatic pressure drop judging means;
operating means for determining a first time differential value of a
front/rear wheel ratio of the rotational angular velocities of the left
tires and a second time differential value of a front/rear wheel ratio of
the rotational angular velocities of the right tires, and determining a
ratio of the first time differential value and the second time
differential value;
one-sided irregular road traveling judging means for judging a traveling
condition of the vehicle, to determine a variation in road conditions
between left and right sides of the vehicle, based on the ratio of the
first time differential value and the second time differential value
determined by the operating means when the vehicle is operating under
one-sided irregular road traveling conditions, and for generating a
judgment result output; and
means for inhibiting the pneumatic pressure drop judging means when the
one-sided irregular road traveling judging means indicates a variation in
road conditions between left and right sides of the vehicle.
10. A tire pressure drop alarm device according to claim 9, wherein the
one-sided irregular road traveling judging means comprises means for
performing integral processing on the ratio of the first time differential
value and the second time differential value determined by the operating
means to generate a value upon which the traveling condition of the
vehicle is judged.
11. A tire pressure drop alarm device according to claim 10, wherein the
one-sided irregular road traveling judging means determines a variation in
road conditions exists between the left and right sides of the vehicle,
when the value generated by the integral processing means is greater than
a predetermined threshold value t.sub.1 ; and determines a variation in
road conditions does not exist between the left and right sides of the
vehicle when the value generated by the integral processing means becomes
smaller than a predetermined threshold value t.sub.2, wherein t.sub.1 is
greater than t.sub.2.
12. A tire pressure drop alarm device according to claim 9, wherein the
one-sided irregular road traveling judging means determines a variation in
road conditions exists between the left and right sides of the vehicle,
when the ratio of the first time differential value and the second time
differential value determined by the operating means is greater than a
predetermined threshold t.sub.1 ; and determines a variation in road
conditions does not exist between the left and right sides of the vehicle
when the ratio of the first time differential value and the second time
differential value becomes smaller than a predetermined threshold value
t.sub.2, wherein t.sub.1 is greater than t.sub.2.
13. A tire pressure drop alarm device, comprising:
rotational angular velocity calculating means for calculating rotational
angular velocities of tires provided for corresponding wheels of a
four-wheel vehicle having a front left wheel, a front right wheel, a rear
left wheel, and a rear right wheel;
pneumatic pressure drop judging means for judging whether a tire pressure
drops, based on the rotational angular velocities calculated by the
rotational angular velocity calculating means;
alarm means for generating a signal corresponding to a judgment result
output of the pneumatic pressure drop judging means;
operating means for determining a first front/rear ratio of the rotational
angular velocities of the left tires and a second front/rear ratio of the
rotational angular velocities of the right tires, and determining a time
differential value of a ratio of the first front/rear wheel ratio and the
second front/rear ratio;
one-sided irregular road traveling judging means for judging a traveling
condition of the vehicle to determine a variation in road conditions
between left and right sides of the vehicle, based on the differential
value of the ratio of the first front/rear wheel ratio and the second
front/rear wheel ratio determined by the operating means when the vehicle
is operating under one-sided irregular road traveling conditions, and for
generating a judgment result output; and
means for inhibiting the pneumatic pressure drop judging means when the
one-sided irregular road traveling judging means indicates a variation in
road conditions between left and right sides of the vehicle.
14. A tire pressure drop alarm device according to claim 13, wherein the
one-sided irregular road traveling judging means comprises means for
performing integral processing on the time differential value of the ratio
of the first front/rear wheel ratio and the second front/rear wheel ratio
determined by the operating means to generate a value upon which the
traveling condition of the vehicle is judged.
15. A tire pressure drop alarm device according to claim 14, wherein the
one-sided irregular road traveling judging means determines a variation in
road conditions exists between the left and right sides of the vehicle,
when the value generated by the integral processing means is greater than
a predetermined threshold value t.sub.1 ; and determines a variation in
road conditions does not exist between the left and right sides of the
vehicle when the value generated by the integral processing means becomes
smaller than a predetermined threshold value t.sub.2, wherein t.sub.1 is
greater than t.sub.2.
16. A tire pressure drop alarm device according to claim 13, wherein the
one-sided irregular road traveling judging means determines a variation in
road conditions exists between the left and right sides of the vehicle,
when the time differential value of the ratio of the first front/rear
wheel ratio and the second front/rear wheel ratio determined by the
operating means is greater than a predetermined threshold value t.sub.1 ;
and determines a variation in road conditions does not exist between the
left and right sides of the vehicle when the time differential value of
the the first front/rear wheel ratio and the second front/rear wheel ratio
becomes smaller than a predetermined threshold value t.sub.2, wherein
t.sub.1 is greater than t.sub.2.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a device for detecting a pneumatic
pressure drop of tires of a four-wheel vehicle in order to give an alarm.
2. Related Background Art
As a safety device for a four-wheel vehicles such as automobiles and
trucks, tire pressure drop detecting devices have recently been proposed,
and some of them have been put to practical use.
A pneumatic pressure drop alarm device has been developed because its
importance is recognized for the reason shown below. That is, when the
pneumatic pressure is low, the temperature of a tire increases due to an
increase of tire deflection. Therefore, the strength of the polymer
material used for the tire is lowered and the tire is more likely to
burst. However, even if the tire is deflated, the driver is often unaware
of the deflation.
As a method of detecting a pneumatic pressure drop by the pneumatic
pressure drop alarm device, for example, there is a method of utilizing a
difference in respective rotational angular velocities F.sub.1, F.sub.2,
F.sub.3 and F.sub.4 (referred to as a "rotational angular velocity F.sub.i
" hereinafter) of four tires W.sub.1, W.sub.2, W.sub.3 and W.sub.4 of the
vehicle. (The tires W.sub.1 and W.sub.2 correspond to left and right front
tires, and the tires W.sub.3 and W.sub.4 correspond to left and right rear
tires, respectively. In addition, these are referred to as a "tire W.sub.i
" hereinafter.)
According to this method, the rotational angular velocity F.sub.i of the
tire W.sub.i is detected every predetermined sampling period .DELTA.T,
based on a signal to be generated by a wheel speed sensor mounted on the
tire W.sub.i. When the dynamic load radiuses (which mean apparent rolling
radiuses of the respective tires calculated by dividing by 2.pi. a travel
distance of the vehicle while the tires make one free revolution) of the
tires W.sub.i are the same, at the same time that the vehicle is traveling
linearly, the rotational angular velocities F.sub.i are the same.
However, the dynamic load radius of the tire W.sub.i varies depending on
the change in pneumatic pressure of the tire W.sub.i. When the pneumatic
pressure of the tire W.sub.i drops, the dynamic load radius becomes
smaller than that at a normal internal pressure. Accordingly, the
rotational angular velocity F.sub.i of the tire W.sub.i becomes higher
than that at a normal internal pressure, thereby making it possible to
detect the pneumatic pressure drop of the tire W.sub.i, based on the
difference in the rotational angular velocities F.sub.i. A judging
equation for detecting the pneumatic pressure drop of the tire W.sub.i is
shown below (see Japanese Laid-Open Patent Publication Nos. 63-305011 and
4-212609).
D=2[(F.sub.1 +F.sub.4)-(F.sub.2 +F.sub.3)]/(F.sub.1 +F.sub.2 +F.sub.3
+F.sub.4) (1)
For example, if it is assumed that the dynamic load radiuses of the
respective tires W.sub.i are the same, the rotational angular velocities
F.sub.i are the same (F.sub.1 =F.sub.2 =F.sub.3 =F.sub.4). Accordingly,
the judging value D becomes 0. Then, threshold values D.sub.TH1 and
D.sub.TH2 are set (D.sub.TH1, D.sub.TH2 >0). When the following judging
expression:
D<-D.sub.TH1 or D>D.sub.TH2
is satisfied, it is judged that the tire W.sub.i having a pneumatic
pressure drop is present. When the judging expression is not satisfied, it
is judged that the tire W.sub.i having a pneumatic pressure drop is not
present. When it is judged that a tire W.sub.i has a pneumatic pressure
drop, an alarm is given by using a display or a speaker.
In the pneumatic pressure drop detection processing at the time of actual
traveling, when front/rear accelerations and left/right accelerations of
the vehicle are large, for example, when the load transfers around the
vehicle at the time of traveling with rapid acceleration or traveling
around a curve, the driving tires are sometimes locked or idled, that is,
the wheel is not rolling due to slippage or some other cause. Since the
locking or idling does not always arise uniformly in left/right driving
tires, revolution counts of the respective driving tires are different. As
a result, D does not become equal to 0, thereby causing a wrong judgment
of reduced pressure. Therefore, for example, there is disclosed a
technique of removing the data corresponding to the rotational angular
velocity F.sub.i in Japanese Utility Model Publication No. 4-11844.
In the technique as disclosed in Japanese Utility Model Publication No.
4-11844, when it is considered that the tire W.sub.i is in the idling or
locking state, the rotational angular velocity F.sub.i to be calculated at
that point is ignored in detecting whether the pneumatic pressure of the
tire W.sub.i drops or not. More specifically, when it is judged that both
ratios F.sub.1 /F.sub.2 and F.sub.3 /F.sub.4 of the rotational angular
velocities F.sub.1, F.sub.2, F.sub.3 and F.sub.4 of the left and right
front tires W.sub.1 and W.sub.2 as well as left and right rear tires
W.sub.3 and W.sub.4 are not within a predetermined range, it is considered
that the tire W.sub.i is in the state of one-wheel idling or locking, and
the data of the rotational angular velocity F.sub.i is ignored.
In the above tire pressure drop detection technique, the rotational angular
velocity F.sub.i calculated when both ratios F.sub.1 /F.sub.2 and F.sub.3
/F.sub.4 are not within the predetermined range is merely ignored.
Therefore, as shown in FIG. 15, if it is judged only by the ratio F.sub.1
/F.sub.2 or F.sub.3 /F.sub.4 when the vehicle is traveling while one side
thereof is running on an irregular road surface (e.g. a shoulder of a
non-paved road such as grassy or sandy place, or a road side covered with
snow) ("one-sided irregular road") because of a car on the opposite lane,
causing idling little by little because the irregular road side is
slippery, there is a possibility of a wrong judging value, since the above
condition is not normally satisfied, at the time of traveling on the
one-sided irregular road. Accordingly, there is a disadvantage in that the
traveling data which is not suitable for the reduced pressure judgment are
adopted, thereby giving a false alarm.
Consequently, it is impossible to judge accurately only by judging whether
the left/right wheel ratios F.sub.1 /F.sub.2 and F.sub.3 /F.sub.4 are
within the predetermined range or not, as disclosed in Japanese Utility
Model Publication No. 4-11844.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a tire pressure drop alarm
device capable of inhibiting a judgment of the tire pressure drop by
accurately judging the situation where the vehicle is traveling on an
one-sided irregular road, thereby accurately detecting the tire pressure
drop.
In order to accomplish the above object, the tire pressure drop alarm
device of the present invention comprises operating means for determining
a time differential value of a front/rear wheel ratio of rotational
angular velocities of left tires and a time differential value of a
front/rear wheel ratio of rotational angular velocities of right tires,
and then determining a difference in or a ratio of the time differential
values of the front/rear wheel ratios between left and right sides, and
one-sided irregular road traveling judging means for judging a traveling
condition which varies in road condition between left and right sides,
based on the difference in or the ratio of the front/rear wheel ratios
between left and right sides determined by the operating means, wherein
the judgment by pneumatic pressure drop judging means is inhibited when it
is judged that traveling conditions vary because of different road
conditions between left and right sides (claim 1).
According to this embodiments, when the vehicle is traveling on a road
which varies in condition between left and right sides, a front/rear ratio
of rotational angular velocities of the tires on one side changes more
markedly than that of rotational angular velocities of the tires on the
other side, and a large time differential value appears. Therefore, it is
possible to judge the varying traveling road condition between left and
right sides. When it is judged that the condition varies between left and
right sides, there is a possibility that the tire rotation of four wheels
may become an unbalanced state and give a false alarm. Then, a judgment by
the pneumatic pressure drop judging means is inhibited to prevent an
issuance of a false alarm, thereby making it possible to certainly detect
the tire pressure drop.
The one-sided irregular road traveling judging means may judge the
traveling condition which varies in road condition between left and right
sides, based on a value obtained by integrating the difference in or the
ratio of the time differential values of the front/rear wheel ratios
between left and right sides, determined by the operating means (claim 2).
Even if the traveling condition which varies due to the road condition
difference between left and right sides is temporarily judged, the
influence of this judging is not exerted on the final determination
because it is first subject to integral processing. Therefore, it is
possible to get rid of an unstable condition attendant on the judgment of
the pneumatic pressure drop.
The one-sided irregular road traveling judging means may judge the
traveling condition which varies in road condition between left and right
sides, when the value obtained by subjecting the difference in or the
ratio of the time differential values of the front/rear wheel ratios
between left and right sides determined by the operating means to the
integral processing is greater than a predetermined threshold value
t.sub.1, and judges the traveling condition which is the same road
condition between the left and right sides when the difference in or the
ratio of the time differential values of the front/rear wheel ratios
between left and right sides becomes smaller than a predetermined
threshold value t.sub.2 (t.sub.2 <t.sub.1) (claim 3).
It sometimes happens that the value subjected to the integral processing
does not damp easily, even if the vehicle has already transferred from the
traveling condition which varies in road condition between left and right
sides to a normal traveling condition. Therefore, when the difference in
or the ratio of the time differential values of the front/rear wheel
ratios between left and right sides becomes smaller than the predetermined
threshold value t.sub.2 (t.sub.2 <t.sub.1) after comparing them, the road
condition is judged to be the same between the left and right sides. And
the value subjected to the integral processing is cleared forcibly.
Thereby, it is possible to rapidly judge a tire pressure drop by the
pneumatic pressure judging means after the vehicle moves from the
traveling condition which varies in road condition between left and right
sides to the normal traveling condition.
The one-sided irregular road traveling judging means may judge the
traveling condition which varies in road condition between left and right
sides, when the value of the difference in or the ratio of the time
differential values of the front/rear wheel ratios between left and right
sides determined by the operating means becomes greater than a
predetermined threshold value t.sub.1 ; and judges the traveling condition
which is the same road condition between the left and right sides when the
difference in or the ratio of the time differential values of the
front/rear wheel ratios between left and right sides becomes smaller than
a predetermined threshold value t.sub.2 (t.sub.2 <t.sub.1).
In this case, the traveling condition which varies in road condition
between left and right sides is judged when the value obtained by the
difference in or the ratio of the time differential values of the
front/rear wheel ratios between left and right sides is greater than a
predetermined threshold value t.sub.1 ; and the judged state can be
maintained even if the vehicle has already transferred from the traveling
condition which varies in road condition between left and right sides to a
normal traveling condition. That is to say, the time constant of the
integral can be regarded as infinite. However, the value of the difference
in or the ratio of the time differential values of the front/rear wheel
ratios between left and right sides is compared with a predetermined
threshold value t.sub.2 (t.sub.2 <t.sub.1). If smaller than the threshold
value t.sub.2, it is immediately judged that the vehicle is traveling on a
road condition which is the same between the left and right sides.
Consequently, it is possible to rapidly judge the tire pressure drop by
the pneumatic pressure judging means after the vehicle in transferred from
the irregular road traveling condition to a normal road traveling
condition.
In addition, the tire pressure drop alarm device according to claim 5
merely differs from the invention according to claim 1 by time
differentiating step, and have the same advantages as those of the
invention according to claim 1.
In addition, the tire pressure drop alarm devices according to claims 6, 7
and 8 merely differ from the tire pressure drop alarm devices according to
claims 2, 3 and 4 by a time differentiating step, and have the same
advantages as those of the pressure drop alarm devices according to claims
2, 3 and 4.
The above objects as well as other objects of the present invention will
become more apparent to those skilled in the art from the following
description with reference to the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram showing the construction of a tire pressure drop
alarm device.
FIG. 2 is a block diagram showing the electrical construction of the tire
pressure drop alarm device.
FIG. 3 is a graph for explaining the judging method of the pneumatic
pressure drop by means of D value.
FIG. 4 is a graph showing the change in a wheel speed of the respective
wheels in case of traveling on the paved road (A), traveling on a road
having irregular driving surfaces on both sides ("both-sided irregular
road") (B), and traveling on the one-sided irregular road (C).
FIG. 5 is a graph showing the situation where the D value becomes an
abnormal large value on the one-sided irregular road in order to exceed
the threshold value for alarm.
FIG. 6 is a graph showing the change in front/rear ratio of rotational
angular velocities of the respective wheels in case of traveling on the
paved road (A), traveling on the both-sided irregular road (B) and
traveling on the one-sided irregular road (C).
FIG. 7 is a flow chart showing a pneumatic pressure drop detection
processing.
FIG. 8 is a graph showing the change in differential front/rear wheel ratio
with time in case of traveling on the paved road (A) and traveling on the
one-sided irregular road (c).
FIG. 9 is a graph showing the absolute value of the change in differential
front/rear wheel ratio between left and right sides with time in case of
traveling on the paved road (A) and traveling on the one-sided irregular
road (C).
FIG. 10 is a flow chart showing a pneumatic pressure drop detection
processing.
FIG. 11 is a graph showing the change in env(.delta.C) and sub(.delta.C)
with time.
FIG. 12 is a graph showing the change in env(.delta.C) and sub(.delta.C)
with time.
FIG. 13 is a flow chart showing a pneumatic pressure drop detection
processing of another embodiment.
FIG. 14 is a graph showing the change in sub(.delta.C) with time.
FIG. 15 is an illustration showing the situation where the vehicle is
traveling while one side thereof is running into an irregular road (e.g. a
shoulder of a non-paved road such as grassy or sandy place, or a road side
covered with snow) because a vehicle is approaching in the opposite lane.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Construction of Tire Pressure Drop Alarm Device
FIG. 1 is a block diagram showing the construction of a tire pressure drop
alarm device. This tire pressure drop alarm device is provided with a
wheel speed sensor 1 having a construction which has hitherto been known,
which is respectively associated with the tires W.sub.1, W.sub.2, W.sub.3
and W.sub.4 of a four-wheel vehicle. Output signals of each of the wheel
speed sensors 1 are supplied to a control unit 2. An initialization switch
3 operated by a driver and a display 4 for indicating a tire having
pneumatic pressure drops are connected to the control unit 2.
FIG. 2 is a block diagram showing the electrical construction of the tire
pressure drop alarm device. The control unit 2 is composed of a micro
computer and its hardware construction includes an I/O interface 2a
required for sending and receiving signals to and from an external device,
a CPU 2b serving as the center of operation processing, a ROM 2c in which
a control operation program of the CPU 2b is stored and a RAM 2d in which
data, etc. are temporarily written to or the written data are read out of
it when the CPU 2b performs a control operation. The RAM 2d is provided
with an area for storing a rotational angular velocity for memorizing a
rotational angular velocity F.sub.i which is effective for initial
correction processing, an area for storing speed values for memorizing a
speed of the vehicle before one period and an area for storing a distance
value for memorizing a traveling distance of the vehicle, as described
hereinafter.
Specifically, each of the wheel speed sensors 1 is provided with a sensor
rotor having a plurality of teeth 49 or 98) inside of the wheel of the
tire W.sub.i, and generates pulse signals corresponding to the number of
teeth by rotating the sensor rotor (referred to as a "wheel speed pulse"
hereinafter). The CPU 2b calculates rotational angular velocities F.sub.1,
F.sub.2, F.sub.3 and F.sub.4 of each tire W.sub.i as well as front/rear
wheel ratios F.sub.1 /F.sub.3 and F.sub.2 /F.sub.4 on the basis of the
wheel speed pulses, every predetermined sampling period .DELTA.T.
The CPU 2b detects a speed V.sub.i of the tire W.sub.i on the basis of the
rotational angular velocity F.sub.i. When the radiuses of all tires
W.sub.1, W.sub.2, W.sub.3 and W.sub.4 are R, a speed V.sub.i is determined
as follows:
V.sub.i =R.times.F.sub.i (2).
The CPU 2b further judges whether the vehicle is traveling linearly or not.
Whether the vehicle is traveling linearly or not is judged based on
whether both differences in or ratios of the rotational angular velocities
F.sub.i of left and right front tires W.sub.1 and W.sub.2 as well as left
and right rear tires W.sub.3 and W.sub.4 exceed a defined value in the
same sign or not. When both do not exceed the defined value in the same
sign, it is judged that the vehicle is traveling linearly.
Pneumatic Pressure Drop Detection Processing
(1) Normal Processing
The pneumatic pressure drop detection processing of the tire W.sub.i is
performed based on the following equation:
D=2[(F.sub.1 +F.sub.4)-(F.sub.2 +F.sub.3)]/(F.sub.1 +F.sub.2 +F.sub.3
+F.sub.4) (3).
In this embodiment, it is judged that the pneumatic pressure has dropped
when the D value calculated from the expression satisfies the following
expression (4) (see FIG. 3):
D<D.sub.TH1 or D>D.sub.TH2 (4)
where D.sub.TH1 and D.sub.TH2 indicate a predetermined constant,
respectively.
In this embodiment, a method is provided for generating an alarm informing
a driver not only that a tire has a pneumatic pressure drop, but also
which tire has the drop in pneumatic pressure. According to the method, it
is first determined that:
the tire having a pneumatic pressure drop is W.sub.1 or W.sub.4 if D <0 in
the equation (3); and
the tire having a pneumatic pressure drop is W.sub.2 or W.sub.3 if D <0.
Furthermore, if the vehicle is traveling linearly, it is determined that:
the tire having a pneumatic pressure drop is W.sub.1 if F.sub.1 >F.sub.2 ;
the tire having a pneumatic pressure drop is W.sub.2 if F.sub.1 <F.sub.2 ;
the tire having a pneumatic pressure drop is W.sub.3 if F.sub.3 >F.sub.4 ;
and
the tire having a pneumatic pressure drop is W.sub.4 if F.sub.3 <F.sub.4.
In such way, after the tire W.sub.i having a pneumatic pressure drop has
been specified, the results are provided to an indicator 4, shown in FIG.
2 as a display. As an example embodiment of the indicator 4, for example,
an indicating lamp corresponding to the tire having a pneumatic pressure
drops among the four tires W.sub.1 to W.sub.4, is turned on. When the tire
cannot be specified, four indicating lamps are simultaneously turned on.
Therefore, it is possible to recognize which tire has a drop in pneumatic
pressure at a glance.
(2) Processing Taking Traveling on One-sided Irregular Road Into
Consideration
Next, processing taking traveling on the one-sided irregular road into
consideration will be explained.
In the above-described pneumatic pressure drop detection processing, when
the vehicle is traveling on the road wherein only one side is slippery,
the D value sometimes exceeds the threshold value, thereby giving an
alarm, even if the tire has a normal internal pressure.
Examining the change in a wheel speed of the respective wheels, using
actual data, the results are as shown in FIG. 4. FIG. 4 shows a graph in
which measured rotational angular velocities of every wheel are plotted
when the vehicle travels on a paved road A, a both-sided irregular road B
(e.g. a gravel road), and an one-sided irregular road C (e.g. tires
traveling on a shoulder on one side).
Referring to FIG. 4, the rotational angular velocities F.sub.i of four
wheels are almost the same when traveling on the paved road A. The
rotational angular velocities F.sub.i of four wheels are almost the same
on average, and change markedly when traveling on the both-sided irregular
road B. This velocity change on the both-sided irregular road is
considered due to unevenness of the road and due to slipperiness of the
road. However, when traveling on the one-sided irregular road C, the
rotational angular velocities F.sub.i of the paved road-side tires are
nearly constant, and the rotational angular velocities F.sub.i of the
driving wheel on the irregular road-side changes markedly in the plus side
of the angular velocity on the paved road, and the rotational angular
velocity of the non-driving or following wheel on the irregular road-side
changes markedly in the minus side of the angular velocity on the paved
road. The reason the angular velocity of the driving and following wheel
on the irregular road greatly shift to plus and minus sides of the angular
velocity of the wheel on the paved road is because the irregular road is
slippery with sand or grass and the driving wheel tends towards spinning
and the following wheel tends towards braking. The reason why the angular
velocity of the driving and following wheel on the irregular road markedly
changes is due to the change of unevenness and slipperiness of the road.
When the D value is calculated based on such data, it becomes an abnormal
large value for the slippery one-sided irregular road as shown in FIG. 5
to exceed the threshold value for alarm, though D normally should be
nearly equal to 0 for normal internal pressure.
In order to prevent a false alarm, it is necessary to detect the situation
of the one-sided irregular road to inhibit the judgment of the D value at
this point (above equations (3) and (4)). This is because the rotational
angular velocity F.sub.i of the slipping tire does not reflect the
internal tire pressure.
In addition, when the front/rear wheel ratio of the rotational angular
velocity during traveling on the paved road A, the both-sided irregular
road B (e.g. a gravel road) and the one-sided irregular road C (e.g.
one-side tires traveling on a shoulder) are detected, the results are as
shown in FIG. 6. The front/rear wheel ratios of left and right sides are
almost the same on the paved road A. The front/rear wheel ratios of left
and right sides are remarkably changing on the both side irregular road B.
However, when the vehicle is traveling on the one-sided irregular road C,
the front/rear wheel ratio on the irregular side is rapidly changing. In
such a condition that the vehicle is traveling on the one side-irregular
road, it is not possible to precisely detect a tire pressure drop because
of the slip of wheel on the irregular side. But one can detect an one-side
irregular road condition by the use of a phenomenon of rapid changing of
the front/rear wheel ratios on the irregular road side as explained above.
Accordingly, it becomes possible to prevent a false alarm by prohibiting
the tire pressure drop detection process when it is detected that the
vehicle is traveling on a one-side irregular road.
Hereinafter, the pneumatic pressure drop detection processing to be
performed in this embodiment will be explained with reference to the flow
chart (FIG. 7).
Firstly, the front/rear wheel ratio F.sub.1 /F.sub.3 and the front/rear
wheel ratio F.sub.2 /F.sub.4 are represented by C.sub.L and C.sub.R,
respectively.
The CPU 2b calculates front/rear wheel ratios C.sub.L =F.sub.1 /F.sub.3 and
C.sub.R =F.sub.2 /F.sub.4 of the rotational angular velocities of the
respective tires W.sub.1, W.sub.2, W.sub.3 and W.sub.4 every predetermined
sampling period .DELTA.T (e.g. one second) (step S1) to determine
differences C.sub.L -C.sub.L' and C.sub.R -C.sub.R' between C.sub.L and
C.sub.R and front/rear wheel ratios C.sub.L' and C.sub.R' which were
calculated last time, i.e. one period previous (step S2). Such differences
are referred to as a "differential front/rear wheel ratio" .delta.C.sub.L
and .delta.C.sub.R, respectively. That is,
.delta.C.sub.L =C.sub.L -C.sub.L' (5)
.delta.C.sub.R =C.sub.R -C.sub.R' (6).
The reason why the differential front/rear wheel ratios are determined is
to know the remarkableness of the change in front/rear wheel ratio.
FIG. 8 is a graph showing the change in a differential front/rear wheel
ratio with time. When it is traveling on the paved road (A), the
differential front/rear ratios of left and right sides are smoothly
changing similarly. When it is traveling on the one-sided irregular road
(C), the differential front/rear wheel ratio at the paved road side is
changing smoothly, while the differential front/rear wheel ratio at the
irregular road side is changing up and down markedly.
The CPU 2b determines the difference between .delta.C.sub.L and
.delta.C.sub.R, i.e., the difference in differential front/rear wheel
ratios between left and right sides to take an absolute value (step S3).
sub(.delta.C)=.vertline..delta.C.sub.L -.delta.C.sub.R .vertline.(7)
The reason why the difference between left and right sides is determined is
to remove the influence of the change in a front/rear wheel ratio at the
time of accelerating/decelerating.
The CPU 2b plots the absolute value sub(.delta.C) of the difference in the
differential front/rear wheel ratios of left and right sides to determine
an envelope of the change with time.
FIG. 9 is a graph showing the change in the absolute value sub(.delta.C) of
the difference in the differential front/rear wheel ratios with time. When
the vehicle is traveling on the paved road (A), the differential
front/rear wheel ratios compensate each other between left and right
sides; therefore, sub(.delta.C) is approximately equal to 0. When it is
traveling on the one-sided irregular road (C), the differential front/rear
wheel ratios are changing markedly, since they cannot compensate each
other between left and right sides. Accordingly, the envelope appears
significantly.
The value of the above envelope is represented by env(.delta.C).
The env(.delta.C) is determined as follows. The env(.delta.C) of the last
time is compared with the sub(.delta.C) of this time (step S5), and
env(.delta.C)=sub(.delta.C), if
sub(.delta.C).gtoreq.env(.delta.C).times..alpha. (step S7);
env(.delta.C)=env(.delta.C).times..alpha., if
sub(.delta.C)<env(.delta.C).times..alpha. (step S6). In the above
equations, .alpha. is a damping constant, and it becomes, for example, a
value of about 0.99.
In such a way, the value of the envelope (output value of an integral
circuit having a fixed time constant) env(.delta.C) can be determined.
The env(.delta.C) of this envelope is taken as the one-sided irregular road
traveling judging value.
The reason why the value of the envelope is adopted is as follows. When the
idling of the wheel on the one-sided irregular road continues for a long
period, the sub(.delta.C) sometimes becomes small because it is a
differential value although the difference in front/rear wheel ratios
between left and right sides is large. Therefore, judging only by the
difference sub(.delta.C) in differential front/rear wheel ratios between
left and right sides, it is likely to judge wrongly that it is traveling
normally.
The CPU 2b compares the one-sided irregular road traveling judging value
env(.delta.C) with the fixed threshold value t.sub.1 (step S8) and judges
that the vehicle is traveling on the one-sided irregular road (step S10)
to stop the tire pressure drop detection processing when the one-sided
irregular road traveling judging value env(.delta.C) exceeds the fixed
threshold value t.sub.1. When the one-sided irregular road traveling
judging value env(.delta.C) does not exceed the fixed threshold value
t.sub.1, it is judged that the vehicle is traveling on the normal road
surface (step S9) to perform the tire pressure drop detection processing.
Further, since the damping constant .alpha. is nearly equal to 1, the
one-sided irregular road traveling judging value env(.delta.C) does not
damp easily; the situation where it exceeds the threshold value t.sub.1
sometimes continues for several minutes, even if the normal traveling has
set in after the one-sided irregular road traveling has finished. The tire
pressure drop detection cannot be performed during that period; however,
in view of the object of the tire pressure drop detection, it may be
considered to be a shortcoming, even if the detection cannot be performed
for a short period of time.
However, it is possible to provide an wherein the tire pressure drop can be
detected immediately when normal traveling has resumed after the one-sided
irregular traveling was finished. According to this embodiment, the
difference sub(.delta.C) in differential front/rear wheel ratios between
left and right sides is always checked. Even if the one-sided irregular
road traveling judging value env(.delta.C) does not damp easily, it is
judged to be traveling on the normal road surface to perform the tire
pressure drop detection processing, if the situation where the
sub(.delta.C) is small continues.
FIG. 10 is a flow chart showing pneumatic pressure drop detection
processing based on this embodiment.
Explaining with this current, calculation of the front/rear wheel ratios
C.sub.L and C.sub.R, calculation of the differential front/rear wheel
ratios .delta.C.sub.L, .delta.C.sub.R and calculation of the absolute
value sub(.delta.C) of the difference in differential front/rear wheel
ratios between left and right sides are the same as those of the flow
chart of FIG. 7.
Next, the normal surface road judgment based on the sub(.delta.C) is
performed (steps S41 to S45).
In the step S41, it is judged whether the sub(.delta.C) is less than the
predetermined threshold value t.sub.2 or not. When sub(.delta.C) is
greater than the predetermined threshold valve t.sub.2, the count value
CNT is cleared to 0 (step S42) and the process proceeds to step S5. When
the sub(.delta.C) is less than the predetermined threshold value t.sub.2,
the count value CNT is moved up by 1 (step S43) to judge whether the count
value CNT is larger than a predetermined number M or not (step S44). When
the count value CNT becomes larger than the predetermined number M, the
one-sided irregular road judging value env(.delta.C) is 0 (step S45). When
the sub(.delta.C) is more than the predetermined threshold t.sub.2, the
count value CNT is cleared to be 0 to go to the step S5.
The predetermined threshold value t.sub.2 is a threshold value for judging
that the vehicle is traveling on the normal road surface when the
situation where the sub(.delta.C) is small continues to perform the tire
pressure drop detection processing even if the one-sided irregular road
traveling judging value env(.delta.C) does not damp easily, and is a value
smaller than the threshold value t.sub.1 of the one-sided irregular road
traveling judging value env(.delta.C). The predetermined number M is a
number used in the situation where the sub(.delta.C) continues to be
smaller than the threshold value t.sub.2, which is required for judging
that the vehicle is traveling on the normal road surface. Accordingly,
even if the sub(.delta.C) happens to become smaller than the threshold
value t.sub.2 due to the influence of noise, etc, the env(.delta.C) will
not become 0 due only to that.
In addition, even if the vehicle is traveling on the normal road surface,
the sub(.delta.C) sometimes exceed the threshold value t.sub.1 temporarily
due to the partial irregularity of the road surface. Also in this case,
the env(.delta.C) does not damp easily, and therefore, the tire pressure
drop detection processing is sometimes prevented. This case has also an
advantages that the vehicle is judged to be traveling on the normal road
surface to perform the tire pressure drop detection processing, if the
situation where the sub(.delta.C) is small continues, as described above.
In the steps S5, S6 and S7, the processing for determining the value of the
envelope env(.delta.C) is performed, similar to the flow chart of FIG. 7.
In the steps S8, S9 and S10, the vehicle is judged to be traveling on the
one-sided irregular road or normal road surface by comparing the value of
the envelope env(.delta.C) with the threshold value t.sub.1.
The above processing according to the flow chart of FIG. 7 will be
explained using the graph (FIG. 11) showing the change in the
env(.delta.C) and the sub(.delta.C) with time, and the processing
according to the flow chart of FIG. 10 will be explained while making a
comparison with the above, using the graph (FIG. 12) showing the change in
the env(.delta.C) and the sub(.delta.C) with time.
Referring to FIG. 11, env(.delta.C) does not damp easily with time even if
the sub(.delta.C) is lowered at the time X. Therefore, the time Y where
the env(.delta.C) becomes lower than the threshold value t.sub.1 becomes
far later than the time X.
Referring to FIG. 12, the processing for comparing the sub(.delta.C) with
the predetermined threshold value t.sub.2 is added, and therefore, the
sub(.delta.C) is lowered at the time X. In addition, when the situation
where the sub(.delta.C) is smaller than the threshold value t.sub.2
continues M times, the env(.delta.C) is forced into 0. Accordingly, when
the vehicle transfers from the one-sided irregular road traveling to the
normal road surface traveling, it is possible to follow this easily.
In the above embodiment, the damping constant .alpha. was assumed to be
less than 1 (.alpha.<1). However, the invention can employ the case when
.alpha.=1. .alpha. is preferably close to 1 or equal to 1, for the sake of
rejecting one-side irregular road data. When .alpha.=1, if sub(.delta.C)
is once over the threshold value t.sub.1, env(.delta.C) does not reduce,
and the tire pressure drop detection is impossible forever. To avoid such
a defect, as shown in the flow chart of FIG. 13, if sub(.delta.C) is below
the predetermined threshold t.sub.2, for M times, it is judged that the
vehicle is traveling on a normal road (step S46). Accordingly, if the
vehicle travels from an one-side irregular road to a normal road, the
process follows such condition immediately. If sub(.delta.C) is over the
threshold t.sub.2, and is over the threshold t.sub.1, it is judged that
the vehicle is traveling on an one-side irregular road (step S48). If
sub(.delta.C) is over the threshold t.sub.2 and is below the threshold
t.sub.1, judgment is held reserved. The advantage of this embodiment is
that the algorithm becomes simple and that memory can be saved since
env(.delta.C) is not necessarily calculated.
FIG. 14 is a graph showing a process of the above flow chart (FIG. 13).
With this graph, sub(.delta.C) is reduced at the time X, and if
sub(.delta.C) is below the threshold t.sub.2 for M times, the processor
judges the vehicle is traveling on normal road and tire pressure drop
detection is released from the prohibited state to an enable state. So,
the processor can rapidly follow from an one-sided irregular road
traveling condition to a normal road traveling condition.
Finally, various modifications will be described.
In the form of the above embodiment, the CPU 2b determined the difference
in differential front/rear wheel ratios between left and right sides, but
the ratio of these may be determined.
In the form of the above embodiment, the difference between .delta.C.sub.L
and .delta.C.sub.R, i.e., the difference in differential front/rear wheel
ratios between left and right sides is determined after the differential
front/rear wheel ratios .delta.C.sub.L and .delta.C.sub.R were determined.
To the contrary, the difference between last period and this period may be
determined after the difference in front/rear wheel ratios between left
and right sides was determined.
In the above embodiment, the value of the envelope is adopted as the
one-sided irregular road traveling judging value. Otherwise, a transfer
average value for some periods may be determined to take as a one-sided
irregular road traveling judging value. In addition, the number of times
that the sub(.delta.C) exceeds the threshold value in a predetermined time
may be counted to take its counted value as the one-sided irregular road
traveling judging value.
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